I already know this is a touchy subject and each firearm owner will have their choice caliber for defense. I will try to not step on any toes and give an honest opinion on the main calibers of choice. The most popular choices are 9mm, .40, and 45 Auto for self-defense.
First, a brief history lesson.
The 9mm Luger was introduced to the market by Georg Luger in 1902, he wanted a compact round that was lethal at 50 meters. Today, the 9mm is the most popular handgun cartridge used by military forces around the world.
The .40 S&W was developed to duplicate the performance of the FBI’s reduced velocity 10MM cartridge and fit into medium frame (9mm size) semi-automatic handguns. It was released in 1990. Ironically, the Glock 22/23 pistols chambered in the .40 S&W were announced one week prior to Smith and Wesson’s 4006 handgun chambered in the .40 S&W. Glock pulled a sneaky move and largely took over the market for handguns chambered in .40 at the time.
The .45 ACP, also known as the .45 Auto was invented by John Browning in 1905. “ACP” stands for Automatic Colt Pistol. Colt submitted their firearm with John Browning, and after successful military trials the Colt 1911 came about firing John Browning’s 45 ACP. The Colt 1911 was used in the US military for many decades due to its reliability and the powerful force of the bullet.
Prior to the .40S&W - the 9mm, .38 special, and .45 were the main cartridges used by law enforcement and military personnel in the United States. The idea behind the .40 was to combine the best characteristics of all these cartridges. It carries a heavy bullet at a high velocity yet doesn’t have the powerful recoil that the .45 has. The 9mm has a very light recoil, but it doesn’t have the knock down power of the 40 cal and 45 cal. Law Enforcement and the Military frequently complain about how smaller calibers have a lack of “knock down” force compared to the 40 the 45. Even though most Government agencies cannot use self defense rounds for duty, civilians have a wide assortment of options that are increasing the “knock down” power of smaller calibers such as the 9mm or even the .380 Auto. When it comes to price of ammunition, 9mm is the cheapest and seems to have the widest variety of loads when browsing ammunition isles of local gun stores here in Utah.
Here is a slight tangent, did you know that hollow jacketed bullets are not ideal for defense against big game? Bears, moose, and other large game animals have very tough and thick hides that slow the bullet down immediately, and if a self-defense round were to make it that far and hit the rib cage or shoulder bones of one of these animals, the bullet would stop dead in its tracks. Flat nose gas checked bullets, semi-wadcutters, and other lead or hard cast bullets are more ideal for defense in the wilderness rather than a bullet that expands upon impact. When defending yourself against large game, you want the bullet to maintain its shape and penetrate as far as possible through the animal’s torso to deliver some serious damage to their internal organs. Buffalo Bore, HSM, and Core Lock seem to be the leading ammunition brands for big game defense and hunting for revolvers and other handguns. If your looking for some extra defense for the outdoors, I would check in with the 3 ammunition brands I just outlined. I personally use a 325-grain HSM wide flat nose gas check through my Smith and Wesson .460 5-inch revolver when I head out into the Uintah’s of Northern Utah. My 5-shot revolver sends the bullet out of the barrel at 1824 fps with 2402 ft lbs. of force.
Anyway, back to the subject at hand, with the modern-day ammunition available at most local gun stores, we have a very wide assortment of reliable defense ammo that can defend us in most circumstances. Whether you’re using a 9mm, .40S&W, or a 45ACP, with the right ammunition, the caliber of bullet will perform as you need it. I leave it up to you to make the choice. I typically carry a 9mm Glock 19 with a 115 grain Hornady self-defense load in my StealthGearUSA Ventcore IWB Mini holster.